The present invention relates to a hydraulic tensioner. More particularly, the present invention, in several different embodiments, relates to a hydraulic tensioning device for maintaining the tension in a chain in an engine timing drive. The tensioner includes a piston or plunger member that extends outward from a housing or body and presses against a chain. The piston is forced outwardly from the housing by a spring located inside the piston. Oil is permitted to flow from a reservoir into the piston through a one-way check valve. Thus, the piston can extend to impart tension to the chain, but retracts slowly.
In one embodiment, the present invention relates to a tensioner that applies proper tension force to a chain or engine belt and, specifically, it relates to a tensioner with a stopper construction that can hold the plunger in the retracted position before assembly of the tensioner.
In general, a tensioner has a housing, a piston or plunger that slides within a cylindrical opening in the housing, and a coil spring that constantly pushes the plunger in the protruding direction. The end of the plunger presses against the tensioner arm due to the spring force of the coil spring.
A stopper member is utilized to hold the plunger in the retracted position before assembly in order to ease assembly of the tensioner to the engine. One end of this stopper member is rotatably supported by the housing and its other end is freely engageable with a stopper pin fixed to the plunger.
In several embodiments, the present invention is directed to a tensioner which is compact, and minimizes wear of the stopper member.
Hydraulic tensioners are also used conventionally for the suppression of fluttering of the chain or belt due to engine torque fluctuations and reduction of noise, vibration and wear of guides and other components.
Hydraulic tensioners are conventionally comprised of a hollow housing with an opening at one end and a hollow plunger with an opening on its rear end side. The plunger slides within the opening in the housing and a spring pushes the plunger in the outward direction by pressure-contacting its one end to the wall of the opening in the housing, and the other end to the wall of the opening in the hollow plunger, respectively. In addition, an oil chamber is formed by the opening in the housing and plunger. The tip of the plunger contacts the tensioner arm located on the slack side of the chain or belt.
During operation of such a hydraulic tensioner, the hydraulic pressure acts on the rear-end side of the plunger in the oil chamber, and the plunger pushes the chain or belt via the tensioner arm, based on mutual action of the hydraulic pressure and spring force. The plunger also receives a force in the reverse direction when the tension of the chain or belt increases during engine operation. During the time when insufficient oil is supplied to the oil chamber, such as immediately after engine starting, or the hydraulic pressure is insufficient in the oil chamber because of low engine rotation speed, the plunger backs up easily and proper tensioning force cannot be applied to the chain or belt.
Therefore, the spring force needs to be set to a higher value to maintain a proper tensioning force on the chain or belt by preventing the retraction of the plunger.
However, in the conventional hydraulic tensioner, the diameter of the plunger is increased because of installation of the spring within the hole of the hollow plunger, and the area of the plunger that receives pressure is large. Consequently, as mentioned above, the tensioning force due to the combination of hydraulic pressure and the spring force becomes unnecessarily high in the normal operation range of the engine when the spring force is set higher, and friction loss increases. As a result, wear increases on the tension arm, guide, and other components.
Therefore, in the conventional hydraulic tensioner, a ratchet mechanism is provided separately to prevent return of the plunger and the spring force is reduced to obtain smaller friction loss. As a result, the construction becomes complex and the cost also increases.
In a second embodiment, the present invention is directed to such problems and its purpose is to offer a hydraulic tensioner which can prevent retraction of the plunger and reduce friction loss with a simplified construction.
In yet another embodiment, the present invention relates to the so-called air vent mechanism for discharging air that mixes in the oil chamber of the housing to the outside of the housing.
In a conventional hydraulic tensioner, air can be mixed with the hydraulic oil in the oil chamber and, in such a case, the plunger retracts when a tension force is applied to the chain or belt due to the compression of the mixed-in air which is a compressible fluid. As a result, vibration occurs in the chain or belt.
Therefore, various air vent mechanisms have been proposed for the discharge of the mixed-in air in the oil chamber to the outside of the housing. A conventional air-vent mechanism, as shown in Japanese Patent Showa 46-28575, for example, uses a sintered filter of a sintered alloy, but dust in the air or sludge in the hydraulic oil can clog the pores of such a sintered filter, which makes air discharge unstable.
Therefore, an air-vent mechanism that discharges air through an air-venting part on the outer periphery where a helical groove is machined, as shown in Utility Model Showa 60-30507, has been proposed to eliminate such a problem. However, in such a case, a separate air-venting part is needed for venting the air, which increases the number of parts and makes the construction more complex.
In one embodiment, the present invention addresses such problems relating to air venting of the chamber.
In yet another embodiment, the present invention relates to a check-valve. Specifically, it relates to a check-valve which is attached from the outside to an opening formed in a housing of a hydraulic tensioner having a housing and an extendable/retractable plunger.
In conventional tensioners, an opening for the introduction of external hydraulic pressure is formed in the housing and a check-valve that regulates the flow of the hydraulic oil and allows it to flow into the oil chamber, but prevents reverse flow, is provided to the opening from the outside.
A conventional check-valve for a hydraulic tensioner 400, as shown in FIG. 32, for example, is comprised of body 403 attached to opening 402 formed in housing 401 of the hydraulic tensioner and ball 404 stored in body 403. Spring 405 has one end in pressure contact with ball 404 to keep ball 404 pressed constantly towards seat surface 406 by the force of spring 405. The other end of spring 405 is supported by bottom wall 407 of body 403. That is, bottom wall 407 acts as a retainer of spring 405. Also, small hole 408 leading to oil chamber of hydraulic tensioner 400 is formed in bottom wall 407.
In such a hydraulic tensioner with a check valve, a decrease in pressure in the oil chamber as a result of a shock or lessening of tension in the chain or belt causes ball 404 to lift from seat 406 and hydraulic oil is supplied to oil chamber through small hole 408. When a tensioning force is applied to the chain or belt and pressure in the oil chamber increases, the pressure is applied through small hole 408 to body 403 and, thereby, ball 404 contacts seat 406, and reverse flow of hydraulic oil is prevented.
In such a conventional check valve 400, hydraulic oil is introduced to oil chamber via small hole 408 formed in bottom wall 407 of body 403. Accordingly, flow resistance is large and sometimes hydraulic oil cannot be introduced smoothly to the oil chamber, and in such cases the response of the hydraulic tensioner decreases. Also, since body 403 is press-fit to opening 402 formed in housing 401, high accuracy machining of inner surface of opening 402 and outer surface body 403 is required, which increases the machining cost of the tensioner. In addition, check valve 100 can slip from opening 402 when pressure in the oil chamber becomes too high and overcomes the press-fitting.
In one embodiment, the present invention is directed to such problems, and its purpose is to offer a check valve for a hydraulic tensioner with which hydraulic oil can be introduced smoothly to the oil chamber of the hydraulic tensioner and slipping of the check valve can be prevented and assembly to the hydraulic tensioner is simplified.